Fusible blowout plug



March 24, 1942. 1.. .o. THOMPSON FUSIBLE BLOW OUT PLUG Filed April 26, 1959 ATTORNEYv Patented Mar. 24, 1942 UNITED STATES PATENT FIC ft" 2,277,533 FUSIBLE BLOWOUT. PLUG Lester 0. Thompson, Oklahoma City, Okla. Application April 26, 1939, Serial No. 270,127 Y 2 Claims. 01. 122-5043) The invention relates to fusible blow-out plugs for use as a safety feature in connection with steam boilers, and particularly relates to improvements over United States Patent Number 1,948,056, which was issued to me on February 20, 1934.

The function of all boiler fuse-plugs is to melt out when the boiler water reaches a dangerously low level, so that the internal pressure in the boiler is relieved and an explosion is thus prevented. Blow-out plugs are usually located in the boiler crown-sheet and fire-box walls so that when the fusible metal is melted, the escaping steam is discharged upon the fire.

The increasing tendency toward the use of extremely high steam pressure in present type boilers has made it imperative that, for the sake of safety, fusible blow-out plugs be designed to withstand these high steam pressures. This could, of course, be done by increasing the length of the present plugs, but resorting to the expediency of increasing the length of the meltable mass, the period of time which is required to melt out the fusible metal of the plug is also increased. Since it is the prime office of fusible plugs to melt out quickly when their inner ends, or their portions lying inside of the boiler, cease to be covered with liquid, increase in their length acts to defeat this purpose by lengthening the period of time which they require to melt out.

It is therefore an important object of the present invention to so design a fusible plug that it will withstand higher boiler pressures without lengthening the time required to melt it out.

Another detrimental condition which is present in fusible plugs of usual construction, lies in the fact that the action of the minerals in the boiler Water erodes the soft fusible metal. This erosive action at first acts to pit the flat inner end of the plug, and in time, this pit deepen-s within the tubular shell of the plug until it is so deep that the boiler water ceases to eddy within the shell. Up to that time, the eddying of the water tends to prevent deposit of minerals in the shell, but as the eddying diminishes, the minerals precipitate and form in the shell. At the time the minerals first begin to form in the shell, there is some eddying effect present but the effect is not sufficient to Wash the deposit out of the shell. The result is that a small amount of the mineral forms a minute ball in the shell and. this ball gradually increases in size as more and more of the minerals are deposited in the shell. Eventually, a pea-sized ball of the mineral is formed in the shell, and this ball is constantly moved and rotated bythe eddy of the Water.

When this condition exists, the ball acts as an abrasive upon the'fusible metal, and the wear thereon increases until such time as the ball has so enlarged in diameter that it will no longer rotate within the shell, or until the pit has so deepened that the eddying effect ceases to be sufliciently strong to move the ball. Whenthis happens, the minerals in the water begin todeposit around the ball, and the bore of the shell is soon bridged solidly by the minerals. The plug then ceases to be capable of functioning should the water level in the. boiler be lowered to the danger point. 1

It is an important object of the present invention to materially lessen eroding of the fusible metal in a blow-out plug by deterring or preventing the original forming of a pit through action of minerals in boiler water.

Other objects of the invention will be apparent from the following descriptive matter with reference to the accompanying one-sheet drawing, wherein:

Figure 1 is a fragmentary elevational sectional .view of one embodiment of the invention;

Figures 2 and 3 are similar views of two other embodiments;

Figures 4, 5 and 6 are elevational sectional views of three different embodiments of the invention;

Figures '7, 8 and 9 are similar views of three other embodiments of the invention; and,

Figures 10, 11 and 12 are perspective views of inner ends of the plugs, which ends are adaptable to all embodiments of the invention.

Like characters of reference designate like parts in all of the figures.

In the'drawing:

The reference numerals l indicates a boiler crown-sheet or plate having an inner surface 2 and an outer surface 3, and being equipped with a through-perforation which is threaded as indicated at 4 to receive a fusible blow-out plug.

In all of the illustrated embodiments, the plug consists substantially of a tubular sleeve or shell 5, preferably having a hexagonal head 6 to engage a wrench, and having an externally threaded portion 1 to be engaged within the threads 4 of the plate I. In each embodiment of the invention, the bore of the shell 5 is filled or partially filled with a fusible core 8 of softer metal than that of the shell, and having a comparatively low melting point.

The elements of the drawing referred to by reference numerals l to 8 inclusive are common to usual blow-out plugs and their installation, and are also common to all embodiments of the invention which are illustrated in the drawing and described herein. The invention per se rests in various changes in the configuration of the bores of the shells, and consequently in the shape of the cores, rests in the extent of the cores with relation to the plates l, and in the particular configurations of the inner ends of the shells 5 and cores 8.

In Figs. 10, 11 and 12 are illustrated three different fragments of inner end portions of the shells 5 and cores 8, which depict shapes applicable to each embodiment of the blow-out plugs illustrated in the other figures. For instance, the plug illustrated in Fig. 1 may be formed in manufacture with an inner end such as illustrated in either Fig .10, 11 or 12, and all of other plugs may be similarly shaped at their inner ends.

In Fig. the inner end of the shell 5 and core 8 are shown as having two oppositely bevelled surfaces H) and H with their point of intersection slightly rounded as indicated at [2.

In Fig. 11 the inner ends of the elements 5 and 8 are similarly shaped, except that the point I3 of intersection has not been rounded off In Fig. 12 the inner end portion of the core and shell are bevelled in a single plane from side to side, thus providing a single bevelled surface M.

The object in providing the bevelled surfaces ll], H and M is to materially defer or entirely prevent the formation of a pit in the inner end of the core 8. Since the boiler water is constantly circulating, the bevelled surfaces are constantly washed by the water, and consequently the mineral precipitate from the water does not as readily form over the end of the core as it would should this end be fiat as it is in usual blow-out plugs. A similar beneficial result could be reached by boring the plate I at an angle and installing a flat ended plug therein. However, this would be a much more expensive operation than merely bevelling the inner ends of the plugs. A somewhat beneficial result could also be obtained by conically pointing the inner end of the shell and core, but this would leave little or no reinforcing around the soft metal core.

Referring now more particularly to the complemental configurations of bore of the shell 5 and the core 8, Fig. 1 illustrates an embodiment in which the bore and core are conically tapered outwardly from their inner ends to a point lying inside of the inner surface 2 of the plate I, which point is indicated by the dotted line AA. From this line, the bore and core extend cylindrically to the outer end of the shell 5.

In Fig. 2 is shown an embodiment in which the bore and core are conically tapered from their inner ends outwardly to a point inside of the boiler and indicated by a dotted line BB, and from this line they are reversely tapered to their outer ends.

Figure 3 illustrates an embodiment of the invention somewhat similar to that illustrated in Fig. 2, but in which the reversely tapered portions of the bore and core meet at a point indicated by a dotted line CC. The line 0-0 lies nearer the inner end of the plug than does the line BB of Fig. 2.

Figs. 4, 5 and 6 illustrate an embodiment in which the bore and core are continuously tapered conically from their inner ends to their outer ends. These figures also illustrate application of the end shapes of Figs. 10, 11 and 12 to this embodiment.

In Figs. 7, 8 and 9 are shown plugs using the end shapes of Figs. 10, 11 and 12 as applied to an embodiment of the invention in which the bore and core are conically tapered from their inner ends to a point D lying adjacent the outer surface 3 of the plate I at which point the core 8 terminates. The bore is conically enlarged from the point D to the outer end of the plug. I

The object of the reverse taper in the various embodiments of the plugs is twofold. First, the portion of the taper lying within the boiler will hold a greater internal pressure than would a straight cylindrical bore. This is also true of the embodiments of Figs. 4, 5 and 6. Second, the flared outer taper, which opens into the boiler fire-box, gives a spreading effect to the water and steam when the plug has melted out due to the water level in the boiler being too low. The effect is to cover more grate surface with the escaping water, and consequently have more of a dampening effect upon the fire in the fire-box.

The length of both tapers may be varied according to the boiler pressures it is desired to accommodate, as well as the portion of the bore of the shell which is to be filled with the fusible core.

I claim:

1. A fuse plug comprising: an elongated shell designed to extend through a boiler sheet; means intermediate its ends for securing the shell to the sheet with one end extending inside of the boiler; a bore extending longitudinally through the shell; and a fusible core closing the bore, the inner end of the plug terminating in a single plane surface lying at an angle in relation to the axis of the plug sufiicient to prevent accumulation of sediment on said surface.

2. A fuse plug comprising: an elongated shell designed to extend through a boiler sheet; means intermediate its ends for securing the shell to the sheet with one end presented to the interior of the boiler; a bore extending longitudinally through the shell; and a fusible core closing the bore, the inner end of the plug terminating in a single plane surface lying at an angle in relation to the axis of the plug sufiicient to prevent accumulation of sediment on said surface.

LESTER O. THOIVIPSON. 

